1. Field of the Invention
This invention relates to the field of electronics. More particularly the invention is directed to electric power supply. By way of further characterization, the invention relates to the supply of AC power to a load by application of a DC control voltage. More specifically, the invention relates to the application of start and run power to an electric motor. By way of specific illustration, but without limitation thereto, the invention will be described as it pertains to the starting of an electric motor in an avionics environment.
2. Description of the Prior Art
A wide variety of motor power feed circuitry are known in the motor control arts. Although each is more or less satisfactory for its intended application, a need in the aerospace arts for a motor control having particular characteristics has been a persistent, and largely unsolved, problem.
One such characteristic is the provision of the necessary start and run voltages. During starting, a high current must be applied to the secondary windings in addition to the primary windings. After start, the voltage to the secondary winding must be reduced.
Another problem area addressed by the invention is the provision of a high degree of isolation between the motor power supply and the DC control current sources. In avionic and space applications the control power is shared by many other circuits and electrical artifacts must not be allowed into the common power source.
Another shortcoming of the known circuitry is the inability to use standard parts to permit hybridization for specific applications. Thus, it is desirable to use standard circuit semiconductor chips rather than the special circuitry as is often required by the prior art devices.
The prior art devices, in general, can operate only over a narrow temperature range. It is considered highly desirable to operate over the temperature range of -55.degree. C. to 100.degree. C. for avionic applications.
It is desirable to have load switching to be electronically controlled. High vibration and G-loadings make governor type switching systems unreliable in these arduous working environs.